This invention relates to a porous shaped article, in particular, sponge-like article, e.g., sponge cloth, of regenerated cellulose which is sufficiently void of impurities to be adapted for medical purposes and also to a process for the manufacture of this shaped article.
Processes for preparing porous shaped articles of cellulose hydrate are known in the art. For this purpose, cellulose is first converted into viscose. In order to cause the formation of pores, a pore forming agent, such as salt grains, e.g. crystals of Glauber's salt of appropriate grain size, are usually incorporated into the viscose, and, if desired, reinforcing fibers, e.g. cotton fibers of 12 to 15 mm length, may be incorporated as well. Then the mass is coagulated in a coagulating bath under the influence of heat, e.g. is coagulated in a water bath at approximately 100.degree. C. In case of preparing a flat shaped porous article, a layer of the mass advantageously is applied to an endless belt, by means of which it is introduced into the coagulating bath. In the water bath, a major portion of pore forming agent is eliminated, e.g. the salt is dissolved and washed away. The porous shaped article then passes through a precipitating bath containing aqueous sulfuric acid and, if appropriate, a chlorite bleaching bath. Next follows a washing step where the porous shaped article is thoroughly washed with water. Then it is dried. After drying, it may be cut to the desired size. Porous shaped articles of regenerated cellulose which are to be used for medical purposes must comply with strict requirements for chemical purity, comparable to the purity standards which are applied to medicinal bandaging material and gauze bandages of cellulose. There have been hardly any difficulties to comply with these requirements as far as the content of dyes, optical brighteners, acids, heavy metal ions, alkali, chlorine ions, sulfate ions, sulfide ions and calcium ions is concerned. However, regarding the degree of turbidity of an aqueous extract from the porous shaped article, such standards cannot be met by the conventional porous shaped articles of regenerated cellulose. The degree of turbidity of the aqueous extract is a measure of the amount of non-fixed cellulose particles which can be washed out of the article. In the case of gauze bandages, the degree of turbidity of the aqueous extract is determined as follows: 10 g of a gauze bandage are placed in a beaker, are covered with 100 ml of boiling hot distilled water and are then heated for fifteen minutes in the boiling water bath. 5 ml of the aqueous extract which is obtained by squeezing or sucking off from the bandage must not be more turbid than the following comparative solution: To 5 ml of a mixture of 2 ml of 0.01 N hydrochloric acid and 98 ml of distilled water, 0.5 ml of 0.1 N silver nitrate solution is added. The comparison is made five minutes after the addition of the silver nitrate solution against a dark background and with impinging light. When the permeability to light of this comparison solution is determined with the aid of a beaker colorimeter (manufacturer: Lange, Berlin) using water as a blank, a permeability value of 85 to 86 percent is obtained, i.e. the aqueous extract of a porous shaped article suitable for medical purposes must have a permeability to light of 85 to 100 percent as compared to clear water; yet, the permeability value of the hereto known porous shaped articles of regenerated cellulose is below 65 percent.
Up to the present, porous shaped articles which have been used in the medical field have been applied only externally as pads, for example, in dental medicine or ophthalmology. It is, however, impossible to use them for surgical purposes, in particular as tampons, since there is a danger that cellulose particles are washed out of the product and are left in the wound and cause inflammations.